Process of applying a decorative surface to a molded article of thermosetting resin



W. S. LAWRENCE PROCESS OF APPLY May 6, 1958 ING A DECORATIVE SURFACE TMOLDED ARTICLE 0F THERMOSETTING RESIN Filed April 23, 1956 IN V EN TOR.fha/felice BY United States Patent j 2,833,685 PROCSSOFAPPLYING-ADECORAIWE SURFACE TO A MOLDED ARTICLE F THERMGSETTING RESINWinthrop S. Lawrence, Landenbe'rg, Pa., assigner to Kaumag'aph Company,Wilmington, Del., a corporationof Delaware Application April 23, 1956,Serial No. 579,950 3 Claims. (Cl. 1541.10)

,/For..examp1e, substantial competition is now-being offered ybymanufacturers of plastic products. to those companies manufacturing thestandard, old-type chinaware.; A long ,recognized `difficulty in theplasticarticle fieldhasvinvolved the inability .to apply a. gooddecorative design-to the'plastic. .Several attempts have been made to.find-a satisfactory .process for axing designs to the plastic articles'but vnone of them have been outstandingly successful and/ oreconomical.

One of thek more recent patents concerned withA the `problem of aliixinga decorativedesign on plastic materials, is U.S.-Patent No. 2,646,380 toBarlow et al, According to that patent, adesign is printed on Va lpaperand. kthe paper, after kresin impregnation, is. placed face down intothe mold used for manufacturing the decorated article. Such process issubject to numerous diiculties.

.For example, since the decorated side. of the paper must beplaced faceydown into lthe mold, theV paper must be of limited. thick-ness in orderto enable the design to s how through properly. On the other hand,sincethe paper must be comparativelythimserious ditlculties areencountered in printing` prior Atcpimpregnation. Moreover, printing mustbe carried out in reverse intthe'prior art procedure (since the printedsurface must berinserted -to -face the preform) while thisydisadvantageous pro-v cedure is eliminatedk by the present invention.These dicultiesr and lothers associated` with4 the prior art areovercome by thepresent invention.

As has been indicated above, the-preparation of decorated sheets for usein the ymanufacture of decorated plastic materials is subject todifficulties( because, among other things, the'paper is inv itselfv tooflimsy and dimen- .sionally unstable to permit accurate sheetprinti-ngin register. According to the present invention; however,

ysatisfactory results by sheet-fed offset lithography, may

be effectedby treating the paper inthe mannerY described below'beforeprinting. Thus, the paper is treated-initially inthe web with athermosetting resin solutionof the same type as that used for the moldedarticle (preferably a melamine formaldehyde resin solution) to obtain a.partialfimpregnation and vcoating Von only one side of the paper. Suchtreatment imparts sufficient rigidity and stability to the paper toenable .a sheet-fed, lithographie printing operation to be carried out.Printing i's effected on the face of the sheet opposite to that'whichhas been partially impregnated and coated. Said untreated face forms anexcellent printing surface since it retains its 2,833,685 "Patented Mayv6, 1958 fibrous nature. Additional improvement stems from the factrthat, since one face is coated and the other `brous, the development ofstatic electricity is retarded; andl stacking and feeding operations arecarried out without` difiiculty. In contrast to a-thoroughly impregnatedsheet,

.one partially impregnatedN and coated on one side only type as -thatused for said'partial impregnation arid coatling (preferably amelamineformaldehyde resin solution) to cover theA printedsurface. This step isdesirable in Vsome cases. The printed sheet, (whether or not furthertreatedonltheprinted surface) is placedin themold whe're a preform hasbeen produced, printed side away from the preform and a blankimpregnated cover 'sheet is placed over it. Impregnationof the coversheet is effected using the same type of resin as that used' forpartially impregnating and coating the sheet on whichV the :decorationis printed. Themold is then closed Vandthe molding cycle is completed.The blank impregnated cove'r sheet is preferably a paper material an'dmay have a thickness up to about 0.01 inch. Using the procedure outlinedabove, the coated printed sheet, aswell as 4the vblank impregnated sheetbecome an inherent part of the nal molded product. The printed colorsareretained beneath the transparent lm'of impregnated-paperand'areextremely vfast to the operations to which it may be subjected.

Formation of articles in accordance with the -invention isy illustratedyby the accompanying drawings in which paper thicknesses in cross-sectionare shown in greatly exaggerated dimensions. v

Fig. l.V is a cross-sectional View showing the various surfaces of theimpregnated and coated paper.

Fig. 2 vis'ian exploded view showing the manner in which the papersheets are placed in the mold;

Fig. 3 is a fragmentary diagrammatic ysectional elevak tion Aof thepartially cured article in thelmold.

Referring to Fig. 1 of the drawing, il represents the melamineformaldehyde coating on the under surface of the paper sheet; 2represents the portion of the under surface of the paper sheetimpregnated with the same melamine formaldehyde resin as that used forcoating; Yand Brepresents the upper yunimpregnat'ed, uncoated sur'- faceof the sheet von which printing is effected. ln'Figs'. 2 and r3, B is atotally impregnated cover sheet, impregnation having been carried outwith the same melamine formaldehyde resin as that used for coating andimpregnating sheet A, described in Fig. 1. Referring again to Fig. 2, Crepresents the base portion df a mold containing molding powder of thedesired type (e. g. melamine formaldehyde); and D represents thecooperating cover portion of the mold. After closing themoldl, 'pressure(preferably about 75-124 tons) is applied and the temperature is raisedto about 12S-150 C. The mold is opened prior to completion of the curingprocess and sheetA is placedin the desired position in the mold with thedecorated surface away from the partially cured article. Sheet B is thenplaced over sheet Afin the indicated manner and curing is completed. Thecoated and printed sheets used in the present`inventionfhaveseveraloutstanding advantages.- Gompied to a fullyimpregnated sheet, they are far more flexible and less friable. Thus,the sheets of the invention, when i used for the decoration of dishes of`substantial depth will more easily conform to the` shape ofthe mold.Substantially no folding results to mar the printed matter and nosignificant cracking is evident in contrast to that which might `beexpected becauseof the friability of a fully impregnated sheet.1 As hasbeen indicated above, the paper coated on one side only resists thedevelopment of static charge and thus may be satisfactorily fed throughthe grippers of the printing machineand readily stacked.` By using ablank impregnated sheet over the printed surface, the inks do not come`in contact `withthe mold and staining by off-set is avoided. j

In order to more fully illustrate the invention, the following specificexample is set forth. It being understood, however, that the example ismerely illustrative t and `that the invention is by nomeanslimitedthereto.

Example Inthe example, the sheets carryingtheprinting are partially`impregnated and/or coated with a melamineformaldehyde resin and are thenused to decorate a plas-` tic material made of the same resin. As hasbeen indicated above, it is`preferable to operate in this manner formaximum effectiveness. Thus, `if a material` were being .molded` of `amelamine `(or phenol) formaldehyde f resin, thepaper containing thedecoration wouldbe impregnated and/or ycoated with a melamine (or`phenol) formaldehyde resin. A

i For coating andpartial impregnation, a solution ofthe followingcomposition (parts are by weight) maybe used:

60pts. melaminevformaldehyde resin (Melmac 405) 1 25 pts. water y 10pts. ethyl alcohol l (2 pts. accelerator [ammonium before use) Thiscomposition is made `up bythe usualprocedure of stirring the resinintothe water at 160 F. containing a portion of the alcohol; is added justbefore use.` The degree ofpenetration of the resin into the'paper can`be controlled by varying the viscositythrough the addition of moreorless water andmay thus be carefully controlled to adjustthepenetration as desired.

Preferably, a rayon paper about .005 inch thick is used. However, thereis considerate `latitude `in this respect since the coating produces theproduct that is heavy enough `and suitable for printing.

In applying the coating to the paper, I find an increase in weight ofabout 25 to 50% is very satisfactory since chloride, etc.] is added someof this penetrates Afurther into the paper under heat` and pressure `inthe molding operation and any excess is squeezed out in the flash.

The melamine-formaldehyde used in the invention may be the Melmac 405mentioned above in the specific working example.` `One may` also use inits place, Melmac `1077 or 1079, each of which melamineformaldehyde resp in contairisalpha cellulose as the filler, has aspecic gravity of 1.5and a tensile strength of 7,000-8,000 lb./ sq.

in.` Also useful` in the invention is the `alpha cellulosefilledmelamine-formaldehyde resin sold by Libbey-Owens- Ford Glass Companyunder the trademark Plaskon This `material also has a specific gravityabout `1.5 and a tensilestrength of about 10,000 lb./ sq. in. As hasbeen million-formaldehyde resin` containing 'nlphav celluloser as Aftersolution, the accelerator thoroughly saturated and taining 50 chloro (orbeta bromo) ethyl urea may be used as socalled latent accelerators.Other accelerators Ysuch as phosphoric acid esters, organic amides andimides (e. g. benzoic acid amide, N-benzoyl succinamide,N-propionylphthalamide, alpha dichlorhydrin, etc. The inks used forprinting the decoration on the coated, partially impregnated paper arethose known to be useful in lithography and fast to heatand formalinvapors. 'They are usually linseed oil varnish suspensions of pigments,such as Pigment Scarlet, Phthalocyamine Blue, Phthalocyarnine Green,Carbon Black, Hansa Yellow, Victoria Blue, Rhoduline Blue, et. Melamineformaldehyde (or equivalent) resins may be added, if desired, forimproving the adhesive characteristics 'of the ink. r

To effect coating and partial impregnation of the sheet whichis to bedecorated, the paper is removed from the roll and permitted to passthrough a series of two or three guide rolls, then over two bars betweenwhich is a tank with an adjustable feed mechanism for feeding the resinsolution (Melmac 405; 60 percent resin solids in aqueous ethanol) ontothe paper.

` sequent printing operation.

the paper sheet used to cover `the t Impregnation "of is effected inaccordance with printed sheet in the mold the standard procedure. Thus,the paper is allowed to i pass through :a bathcontaining a resinsolution (one conpercent melamine-formaldehyde resin solids ie. g.Melmac 4051 in aqueous ethanol is satisfactory). After impregnation thepaper is passed through squeezed rollers to remove the excess resin andthen dried by airdrying or heating at -175" F. m

After the coated and partially impregnated paper has been dried, and cutinto trimmed sheets, the designis printed on the uncoated surface in thestandard lithographic manner and, after the printed surface is dried, itmay be used for attachment to the molded preform material.

For applying the decoration to the preform, the printed sheet is appliedto the mold containing the preform with the printed surface away fromthe preform. A `sheet impregnated with melamine resins is then placedover the printed surface, the mold is closed andthe molding operation iscompleted.

This invention may be variously otherwise embodied within the scope ofthe appended claims.

I claim:

:1. The process of applying a* decorative surface to an article made bycompression molding of a thermosetting resin molding powder whichcomprises impregnating and coating only one surface of an absorbentpaper with a thermosetting resin of the same group as said thermosettingresin molding powder, printing a decorative design on the uncoatedsurface of said absorbentA paper to form a decorated sheet, impregnatinga second absorbent paper, placing said impregnated absorbent paper overthe decorative design on said decorated sheet to form a two-sheetassembly, positioning said Iassembly on the article in the opened moldprior to completion of the curing step with thev decorative design awayfrom said article in said mold, completing the curing step and removingthe molding.

2. The process of claim 1 wherein the thermosetting resinmolding powderis a melamine-formaldehyde molding powder and the thermosetting resinused for impreg nation and coating is a melamine-formaldehyde resin.

3. The process of claim 1 wherein a thermosetting molding powder isadded to the surface of the paper having the decorative design.

(References on following page) References Cited in the file of thispatent 2,410,361

UNITED STATES PATENTS 21646380 1,454,845 Clay May 15, 1923 1,634,830Hargrave July 5, 1927 5 605,643 1,880,930 Elbel et al. Oct. 4, 19322,040,564 Rapley May 12, 1936 2,084,081 Faber June 15, 1937 6 FranceOct. 29, 1946 Barlow et a1 July 21, 1953 FOREIGN PATENTS Great BritainJuly 28, 1948 OTHER REFERENCES Laminating With Melamine Resins,Plastics; December 1946; pages 46, 48, 49, 94 and 95.

1. THE PROCESS OF APPLYING A DECORATIVE SURFACE TO AN ARTICLE MADE BYCOMPRESSION MOLDING OF A THERMOSETTING RESIN MOLDING POWDER WHICHCOMPRISES IMPREGNATING AND COATING ONLY ONE SURFACE OF AN ABSORBENTPAPER WITH A THERMOSETTING RESIN OF THE SAME GROUP AS SAID THERMOSETTINGRESIN MOLDING POWDER, PRINTING A DECORATIVE DESIGN ON THE UNCOATEDSURFACE OF SAID ABSORBENT PAPER TO FORM A DECORATED SHEET, IMPREGNATINGA SECOND ABSORBENT PAPER, PLACING SAID IMPREGNATED ABSORBENT PAPER OVERTHE DECORATIVE DESIGN ON SAID DECORATED SHEET TO FORM A TWO-SHEETASSEMBLY, POSITIONING SAID ASSEMBLY OF THE CURING STEP WITH OPENED MOLDPRIOR TO COMPLETION OF THE CURING STEP WITH THE DECORATIVE DESIGN AWAYFROM SAID ARTICLE IN SAID MOLD, COMPLETING THE CURING STEP AND REMOVINGTHE MOLDING.